A PUF is a physical device or function whose output depends upon the device's physical characteristics. The physical characteristics, such as critical dimensions, doping levels of semiconducting layers, and threshold voltages, make the devices unique and difficult to duplicate. PUF may therefore be utilized as a hardware implementation of a one-way function.
PUFs are strengthening the level of security of emerging data security methods. In such systems, PUFs operate as a set of cryptographic primitives useful in authentication procedures. The underlying mechanism of PUF authentication is the creation of a large number of challenge (i.e. Input) response (i.e. output) pairs (called CRPs) that are unique to each PUF device. Once deployed during an authentication cycles, the PUFs are queried with challenges. Authentication is granted when the rate of matching responses is statistically high enough.
In various authentications, the challenges are stored in a secure server coupled to the device being prepared for authentication. Once generated during the authentication cycles, the challenges are then used in challenge queries. Authentication is granted by the system when the rate of matching responses between the PUF-generated CRPs is sufficiently high enough above a threshold value. Weak PUFs generally only produce a satisfactory rate of responses far from 100% matching, while with strong PUFs the rate approaches 100%.
Over time, however, PUFs are subjected to a set of physical parameters, such as temperature, aging factors, bias voltage drifts, and electrostatic interferences that cause the output of a PUF to change over time. In conventional implementations, this varying output can result in an increased and undesirable error rate. A number of different error correction coding (ECC) techniques have been developed in an attempt to reduce intra-PUF output variations. These approaches, however, generally cannot overcome the relatively high data error rate in subsequent read-outs of PUF in the presence of environmental variations.